tsdb tests: avoid capture-by-reference in goroutines

Only one version of the variable is captured; this is a source of race conditions.

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

tsdb/compact_test.go

@@ -1575,12 +1575,13 @@ func TestHeadCompactionWithHistograms(t *testing.T) {
 func TestSparseHistogramSpaceSavings(t *testing.T) {
 	t.Skip()
 
-	cases := []struct {
+	type testcase struct {
 		numSeriesPerSchema int
 		numBuckets         int
 		numSpans           int
 		gapBetweenSpans    int
-	}{
+	}
+	cases := []testcase{
 		{1, 15, 1, 0},
 		{1, 50, 1, 0},
 		{1, 100, 1, 0},
@@ -1692,7 +1693,7 @@ func TestSparseHistogramSpaceSavings(t *testing.T) {
 				}()
 
 				wg.Add(1)
-				go func() {
+				go func(c testcase) {
 					defer wg.Done()
 
 					// Ingest histograms the old way.
@@ -1740,7 +1741,7 @@ func TestSparseHistogramSpaceSavings(t *testing.T) {
 					oldULIDs, err = compactor.Write(oldHead.opts.ChunkDirRoot, oldHead, mint, maxt, nil)
 					require.NoError(t, err)
 					require.Len(t, oldULIDs, 1)
-				}()
+				}(c)
 
 				wg.Wait()
 

tsdb/head_wal.go

@@ -694,9 +694,9 @@ func (h *Head) loadWBL(r *wlog.Reader, syms *labels.SymbolTable, multiRef map[ch
 
 	go func() {
 		defer close(decodedCh)
-		var err error
 		dec := record.NewDecoder(syms)
 		for r.Next() {
+			var err error
 			rec := r.Record()
 			switch dec.Type(rec) {
 			case record.Samples: